The present invention relates to the refining of crude vegetable oils, and in particular the refining of crude soybean oil, to render the oil useful in industrial applications. Refined vegetable oils and compounds and materials derived therefrom have a number of uses in industrial applications. For example, refined soy oil can be used as an ecological alternative to products derived from petroleum that are used in making urethane foams. One difficulty with using such refined vegetable oils, however, is that the costs associated with the refining process make the refined vegetable oils to expensive to use in industrial applications.
Crude oil that has been extracted from the oil-containing vegetable material is typically a dark colored turbid liquid that needs to be further refined to convert it to a useful oil product. There are a wide variety of known techniques for refining crude vegetable oils into useful vegetable oils. Because most of the refined vegetable oils are intended for human consumption, most of the conventional methods and equipment used in vegetable oil processing are directed to removing impurities that can contribute to unwanted flavor, color, odor, and other undesirable properties. Such impurities include phosphorus-containing contaminants such as hydratable and non-hydratable phospholipids, free fatty acids, color bodies and trace minerals.
The typical known vegetable oil refining process involves several steps, such as degumming, neutralization (alkali refining), bleaching and deodorization. The degumming step typically involves adding water and usually other chemicals, such as phosphoric acid, to the crude oil, heating and agitating the mixture for a period of time (approximately 10-30 minutes) at temperatures of about 50-70° C., and then subsequently centrifuging the mixture to separate the water and oil. The degumming step can be repeated to further reduce the amount of phospholipids in the crude oil.
The degummed oil is then subjected to several additional refining steps to remove other unwanted components such as free fatty acids, color bodies, and other impurities. In these refining steps, the free fatty acids are saponified; the oil is washed to remove the soaps; neutralized; and further washed to remove excess chemicals and soaps. The oil is then bleached to remove color bodies and then finally deodorized. Since an alkali is used to saponify the free fatty acids, the process is known as alkali or chemical refining.
The capital cost associated with equipment to practice these chemical refining steps is very high. For example, centrifuges and filtering equipment, which can be expensive to maintain, are typically used to separate the oil from the washing water. Chemical refining also involves many steps which are cumbersome and which inherently contribute to oil losses, since each of the refining steps produces a residue which carries with it a certain quantity of usable oil, thus decreasing the yield of the refined oil. Because of the high cost of equipment, the high operating expense and the losses of product oil, there has been a desire in recent years to practice a process commonly referred to as physical refining.
In a physical refining process, crude oil, which has been subjected to several pretreatment processing steps, is brought to an elevated temperature (250° C. or more) in a vessel operated under vacuum. Steam is sparged into the oil during treatment. Temperature and retention time conditions are selected such that the free fatty acids and other impurities are volatilized and distilled off. The treated oil is then typically cooled and given a post bleach to further lighten the color of the oil.
Although physical refining offers the advantage of reduced capital and operating costs, it still requires the crude oil to be subjected to substantial pretreating steps, including the addition of chemicals to remove at least some of the impurities in the crude oil. These substantial pretreating steps add to the cost of the physical refining process, making the fully refined oil resulting from the process nevertheless still economically undesirable for industrial applications.
The present invention contemplates a physical refining process that eliminates the substantial pretreatment steps and results in a partially refined vegetable oil that is useful in industrial applications.